1. Field of the Invention
The present invention relates to a fluidized-bed reactor, and more particularly to a fluidized-bed reactor for uniformly oxidizing, i.e. combusting or gasifying, solid material containing combustible material and incombustible material, such as industrial wastes, municipal wastes, or coal, and for stably recovering thermal energy from the oxidized combustible material while smoothly discharging the incombustible material.
2. Description of the Prior Art
As the economy develops, general wastes produced as a result of economic activities are increasing at a rate of 3 to 4% each year, and reach an amount of 50 million tons a year in Japan. An analytic study indicates that 82% of such general wastes are combustible material and correspond to 7.2 million tons in terms of oil.
Industrial wastes keep on increasing year after year. Therefore, plastics including incombustible material, which have heretofore been handled as unsuitable material for combustion and filled in moats, will have to be incinerated in the future because of a limited number of areas available for disposal of such plastics. Combustible industrial wastes including waste oil and waste plastics amount to 17 million tons a year, and should be treated as a fuel rather than wastes because they can produce heat at a ratio of 3000 kcal/kg.
However, it is difficult to stably combust the solid combustible material to utilize its energy because the solid combustible material is available in a wide variety of natures and configurations and contains a large quantity of incombustible material of indeterminate shape mixed therewith. Thus, effective utilization of energy recoverable from general and industrial wastes has not been practiced.
For effectively utilizing energy recoverable from general and industrial wastes, there have been developed a variety of systems for recovering thermal energy from the general and industrial wastes through oxidization including gasification and incineration thereof. Among those developed systems, there is a fluidized-bed incinerator or a fluidized-bed boiler that has been expected to be used as a system capable of stably recovering thermal energy by uniformly combusting solid material containing combustible material and incombustible material while smoothly discharging incombustible material. However, such a fluidized-bed incinerator or a fluidized-bed boiler has been disadvantageous for the following reasons:
When a waste material is combusted in a bubbling type fluidized bed, the waste material cannot uniformly and stably be combusted because solid particles flow only vertically and are not dispersed sufficiently in the bubbling type fluidized bed. The incombustible material whose specific gravity is larger than the fluidized medium is deposited over a wide range on the bottom of the furnace. As a result, it is difficult to discharge the incombustible material from the furnace, and the incinerator or the boiler cannot be operated in a stable condition.
In order to solve the above problems of the simple bubbling type fluidized-bed, there have recently been proposed systems for generating a circulating flow in an enriched fluidized bed with varying fluidizing speeds of the fluidized medium to thereby mix and disperse the solid material to be incinerated for stable combustion.
The solid material to be incinerated by such proposed systems includes various material such as waste tires. Incombustible material in the form of wires produced when waste tires are combusted tends to be deposited on the bottom of the fluidized bed and is liable to be entangled with heat transfer tubes, and hence fluidization of the fluidized medium is not carried out smoothly, resulting in malfunction of the furnace. No effective incineration process has heretofore been available for industrial wastes including incombustible material in the form of wires, such as waste tires.
For incinerating waste material, it is necessary to reduce NOx and other toxic substances produced when the waste material is combusted, to prevent a thermal energy recovery device from being corroded in a reducing atmosphere, and to discharge incombustible material smoothly. However, there have not been available in the art any apparatus which can meet all of the above requirements.